(i) Field of the Invention
The present invention relates to electron beam drawing masks, particularly to electron beam drawing masks including means for compensating proximity effect.
(ii) Description of the Related Art
An electron beam exposure method is an exposure technique in which an electron beam is moved on a resist to scan, thereby directly drawing a circuit pattern. Using this electron beam exposure method, a pattern on a scale of 0.1 xcexcm or less can be drawn with high resolution and high accuracy. For this reason, such an electron beam exposure method is widely used for fine processing, e.g., for pattern formations of photomasks or the like, or wiring formations on semiconductor devices.
In the electron beam exposure method, however, the electron beam having entered a resist film may collide with atoms constituting the resist film so that the beam may be scattered forward. In addition, the electron beam having passed through the resist film may collide with heavy atoms constituting a semiconductor substrate or a wiring pattern so that the beam may be scattered backward. As a result, the forward- or backward-scattered electrons are applied to a resist film area around a target area to be irradiated with the electron beam. This causes a phenomenon that a corner of the drawn pattern is rounded, or a phenomenon that the dimensional accuracy of the pattern is deteriorated due to the variation of pattern density. These phenomena are called xe2x80x9cproximity effectxe2x80x9d because they are apt to appear in general at where the pattern has a narrow interval.
Particularly in case that a wiring pattern or the like made of a material having a high backward scattering coefficient, such as tungsten or molybdenum, is formed as the underlayer of the resist film, proximity effect due to backward-scattered electrons may appear remarkably. Thus, to improve the dimensional accuracy of a pattern in the electron beam exposure method, a proximity effect compensation is required wherein, prior to the irradiation with an electron beam, a calculation is made by a simulation taking the influence of proximity effect into consideration, and thereby the exposure quantity with the electron beam is regulated in advance.
For this proximity effect compensation, the following methods are known: (1) methods wherein the distribution of energy accumulated in the resist film by the electron beam is calculated by a simulation, and, in accordance with the calculated result, a pattern different in shape from a designed objective pattern is made in the mask so as to compensate proximity effect upon actual drawing (mask bias or the like); (2) methods wherein, after a normal pattern drawing operation, separate auxiliary exposure is done to compensate the shortage of energy caused by proximity effect; and (3) methods wherein auxiliary exposure is done using a mask having a membrane structure, as represented by a scalpel ghost method.
Of the above-mentioned proximity effect compensation methods, methods wherein a pattern different in shape from an objective device pattern will be described with reference to FIG. 2. FIG. 2 illustrates a conventional electron beam drawing mask pattern for compensating proximity effect, wherein a device pattern on design is shown in the left part of FIG. 2 and a pattern actually made in a mask is shown in the right part of FIG. 2.
FIG. 2 shows two methods for compensating proximity effect. The upper side in FIG. 2 shows a method wherein, referring to a simulation result of the distribution of accumulated energy of an electron beam, a pattern 9 different in size from a device pattern 1 is made in a mask 10 so that the resist pattern after exposure and development may become the same as the designed pattern. According to this method, proximity effect can be compensated without separately performing auxiliary exposure for compensating the shortage of energy due to proximity effect.
On the other hand, the lower side in FIG. 2 shows a method wherein an auxiliary pattern is added to the device pattern 1 at its circumferential portions for compensating proximity effect. This method corresponds to a technique disclosed in Japanese Patent Application Laid-open No. 2000-68180. According to this technique, fine auxiliary slits 8 for compensating proximity effect are provided at the outermost corner portions of the device pattern 1 to be drawn. Each slit 8 has its width that allows a quantity of electrons, which does not exceed the resolution limit of the resist, to pass through the slit. Auxiliary exposure to the extent of backward scattering diameter is thereby done to compensate proximity effect at the corner portions of the device pattern 1.
In the method of the upper side in FIG. 2, however, because the pattern 9 different in size from the designed pattern must be made in the mask 10, the compare check of the on-mask pattern with the designed pattern can not effectively be done and so the defect check becomes difficult. Besides, there may arise further problems that the data quantity becomes large, a long time is required for making the mask, and the cost increases.
On the other hand, in the method of the lower side in FIG. 2, because fine auxiliary stilts 8 in accordance with an estimation of proximity effect must be provided in the mask 10, in order that such fine auxiliary stilts 8 themselves cannot be resolvable, a complex pattern finer in comparison with the design rule must be formed. This may require processing accuracy higher than that when the original pattern as designed is formed. There arises a problem that it becomes difficult to make the mask.
Besides, the methods wherein separate auxiliary exposure is done to compensate the shortage of energy caused by proximity effect may bring about a decrease in throughput by the time required for the auxiliary exposure process. Further, in the methods wherein auxiliary exposure is done using a mask having a membrane structure, there may arise a problem of deterioration of contrast.
It is an object of the present invention to provide electron beam drawing masks capable of effectively compensating proximity effect without forming any complex pattern finer than a device pattern.
An electron beam drawing mask according to the present invention comprises: a substrate for damping an electron beam to a predetermined quantity of electrons while the electron beam passes through the substrate; a metallic film formed on at least one surface of the substrate for interrupting the electron beam; a main pattern constituted by at least one opening bored through the substrate and the metallic film; and an auxiliary pattern formed near the main pattern and constituted by at least one window portion where the metallic film has been removed to expose the substrate.